Regular maintenance, like replacing your car’s battery, can make it last longer and keep you from dealing with breakdowns when you least want them to. But many car users might need to learn this: replacing the battery can mess up your car’s onboard diagnostics system.
After a new car battery installation, drive 75-100 miles to reset OBD-II readiness monitors in Ready state, use an OBD2 scanner to verify readiness, and then schedule and pass the inspection.
In this article, we’ll explore why a new battery can affect your car’s inspection, what you should do if you encounter this situation, and how to prepare for a successful inspection after a battery replacement.
Table of Contents
Why Does A New Battery Affect Your Car Inspection?
Modern cars have a system called Onboard Diagnostics II (OBD-II) that checks a lot of different parts related to emissions and engine efficiency. The ready monitors are an essential part of this system.
The catalytic converter, oxygen sensors, and evaporative emissions (EVAP) system are some of the parts that these tools keep an eye on. To pass an emissions test, these readiness monitors must be in the “Ready” state.
The OBD-II system’s memory is cleared when you change the battery in your car. This clears the readiness monitor state. If you do this restart, some or all of the monitors might show “Not Ready,” which could mean your car fails an emissions test.
What To Do After Replacing Your Car Battery For Inspection
Now that we understand why a new battery can affect your inspection let’s explore what steps you should take to ensure a successful inspection:
1. Drive Your Vehicle:
It’s essential to drive your car again after changing the battery so the onboard computer can reset all its systems and readiness monitors. These tools are necessary to check how well different emissions control parts work, like the EVAP system, oxygen sensors, and catalytic converter.
Take your car for at least 75 to 100 miles. This far away lets the onboard computer do diagnostic tests in various driving situations, such as the city and highway.
2. Monitor Readiness Status:
If you can access an OBD2 (Onboard Diagnostics II) code reader, you can independently check the readiness status of your car’s monitors. These monitors should show “Ready” to show that the emission control systems have been appropriately checked and are working correctly.
- The misfire monitor looks for engine misfires, which can cause more pollution.
- This device monitors the oxygen sensors that help cars use less gas and reduce pollution.
- Check how well the catalytic converter works to reduce harmful exhaust fumes.
- The EVAP Monitor checks the evaporative emissions device, stopping fuel vapor from entering the air.
- The EGR monitor controls the exhaust gas recirculation system, which lowers nitrogen oxide (NOx) pollution.
3. Keep Records:
Write down the date and mileage of when the new battery was put in and the information about when the old battery was replaced. This information can be helpful during the review and could be used as proof if there are any questions about the new battery.
4. Schedule Your Inspection:
You can set up your state inspection once you’re sure all your vehicle’s ready monitors are set to “Ready.” Ensure you follow the rules and directions in your state regarding inspections, emissions testing, and any paperwork that must be filled out.
The Importance Of Readiness Monitors
Ensuring that all monitors are “Ready,” inspectors can adequately check if a vehicle meets emissions standards.
1. Ready vs. Not Ready Status:
- Ready: This state means that the OBDII system checked a specific emissions control system and is now working as it should.
- Not Ready: If the OBDII system is not ready, it needs to check a specific emissions control system. It means the system still needs to finish its testing or review process.
- N/A or N/S: This state means that the OBDII system does not need to check that particular emissions control system (N/A or N/S). There’s no need to evaluate some systems because they might not work with some cars.
2. Common Reasons For “Not Ready” Monitors:
The most common reason for monitors to be in a “Not Ready” state is that the battery has been disconnected. Several things can cause the battery to break, such as:
- Any maintenance work on the engine that needs the battery to be disconnected can mess up readiness sensors.
- If the battery in your car dies and needs to be replaced, it can restart the monitors.
- Disconnecting the battery is often needed to install a new car radio, which can mess up readiness sensors.
- Adding a new car alarm may require removing the battery, just like installing a radio.
3. Locating Readiness Monitor Status On The Vehicle Inspection Report (VIR):
The Emissions Test Results part of the VIR will indicate if a monitor is “Ready,” “Not Ready,” or in a state of N/A or N/S. Remember that the requirements for a readiness monitor may be different based on the year model of your vehicle:
- 2001 and newer vehicles: One non-continuous monitor can show “Not Ready” and still pass the test, but two or more “Not Ready” readings will mean the car fails.
- 1996 – 2000 vehicles: These cars can pass the test even if two monitors are simultaneously in a “Not Ready” state. If three or more monitors say “Not Ready,” the car will not work.
Changing Monitors To “Ready”
This is what you can do to help you pass an inspection if you just changed your car’s battery and are having trouble because the readiness monitors aren’t set:
1. Performing A Drive Cycle:
After replacing the battery, you must do a “drive cycle” to set the “ready” devices.
- Ensure your car’s gas tank is about 1/4 to 3/4 full. This is something that many panels need to work on.
- If your car has been sitting for at least eight hours, start when the engine is cold.
- For about 15 minutes, keep the car’s speed between 45 and 65 mph on the highway. This helps set the sensors for the oxygen sensor, the catalyst, and the evaporative system.
- Drive through city traffic for about 10 minutes, stopping and starting a few times. This helps set the monitors for the secondary air system and exhaust gas recirculation (EGR).
2. Using An OBD-II Scanner:
If you have an OBD-II reader, check the readiness monitors to see how they are doing. If every computer says “ready,” you should be able to pass the test.
How To Reset Monitors After Battery Replacement?
If you replaced your car’s battery and are getting “not ready” monitors during your emissions test, there are steps you can take to help reset these monitors and pass the inspection:
1. Ensure A Cold Start:
Start with the engine cold. The engine is usually cold to start when it has been off for a few hours or overnight.
2. Turn Off Accessories:
Before starting the car, turn off all accessories, including the air conditioning and heating system and any electrical equipment added after the car was bought.
3. Ignition On (Engine Off):
Put the key in the “ON” position without starting the engine. Let it stay in this position for about a minute.
4. Start The Engine:
Turn on the engine and let it run for about two minutes without doing anything. Ensure the engine reaches at least 65°C (149°F) in temperature. Drive the car for about eight minutes while keeping the following things in mind:
- The Mass Air Flow (MAF) number ranges from 4 to 30 grams per second.
- Keep the engine speed between 1,000 and 3,000 RPM.
5. Apply The Brake (Automatic) Or Clutch (Manual):
Press and hold the brake pedal while moving if your car has an automatic transmission. Press and hold the clutch pedal if your car has a manual transmission. Drive the car for about two minutes under the following conditions:
- Between 15 and 30 grams per second, the MAF signal.
- RPM is always between 1,200 and 1,500.
Let go of the accelerator pedal, and don’t touch it for two minutes while the car runs.
6. Drive The Vehicle:
Drive the car for about two minutes at 15 mph or less. This step is crucial if you want to finish the EVAP watch. Drive the car at speeds between 28 and 70 mph for at least 5.5 miles, with the car hitting at least 50 mph.
7. Turn Off The Engine:
Stop the car safely, set the parking brake (if the car is automatic) or shift to “Park” (if the car is automated) or “Neutral” (if the car is manual), and then turn off the engine.
For at least 45 minutes, don’t touch the car or turn on the engine.
After 45 minutes, use a scan tool to check the I/M (Inspection/Maintenance) System Status. All signs for the I/M System Status should show “YES.”
How To Pass An OBD-II Inspection After Changing The Battery?
1. Check For Warning Lights:
Before you change the battery, look at the panel to see if any warning lights are on, especially the “Check Engine” (CEL) light. Diagnostic Trouble Codes (DTCs) will be shown. Write them down.
2. Replace The Battery:
Make sure the new battery is installed correctly and firmly. Problems can happen if the battery is loose or not connected correctly.
3. Reset The OBD-II System:
To restart the OBD-II system, unplug the negative (black) terminal of the battery for 15 to 30 minutes. This will eliminate any DTCs that have been saved and reset the readiness monitors. Check your vehicle’s instructions to find out how long you should wait to disconnect the battery from your car.
4. Perform A Drive Cycle:
Once you’ve put the battery back in, you’ll need to do a drive cycle. A drive cycle is a specific set of driving situations that let the vehicle’s OBD-II system reevaluate and set readiness monitors.
If you have an OBD-II scanner or code reader, you can check the readiness monitors’ state from time to time. Ensure the “ready” status is shown on all crucial monitors.
5. Complete The Drive Cycle:
Drive your car according to the directions in the drive cycle until all readiness monitors are in the “ready” state. This could take a while, depending on how you drive and what monitors you have.
6. Schedule The Inspection:
Schedule the OBD-II check once all monitors say they are “ready.” Ensure to do this while the panels are in the “ready” state.
For the OBD-II check, you should take your car to a certified inspection station or technician. Your car should pass the OBD-II inspection if all the monitors are set to “ready” and no danger lights are on.
1. How Many Miles Do You Have To Drive After Replacing The Battery?
Most of the time, you should drive your car for at least 75 to 100 miles after changing the battery so that the onboard computer can reset the systems and readiness monitors. This far away lets the onboard computer do diagnostic tests in various driving situations, such as the city and highway.
2. How Long After The Battery Disconnect Is The Car Ready For Emissions?
When the check engine light is on, a car will not pass a pollution test. If the battery has been disconnected or the trouble codes have been cleared, you must drive the car for up to a week in different circumstances before it will pass.
3. Does Changing Car Battery Affect Mileage?
The fuel economy can be affected by a bad or failed battery because the vehicle’s alternator will need to use more horsepower to charge the battery correctly. This extra load puts more pressure on the battery and uses more fuel.
4. How Do I Know If My Drive Cycle Is Complete?
Plug your OBD-II reader into the car’s OBD-II port, usually near the steering column under the dashboard. Check the state of the ready monitor. If all readiness monitors say “Ready” or show green, the drive cycle is over, and your car is prepared for an emissions check.
In conclusion, changing the battery in your car can mess up the ready monitors needed for emissions tests. Follow these steps to pass a check after changing your battery: Drive your car for 75-100 miles to reset the monitors, check the readiness state with an OBD2 scanner, keep records, schedule the inspection when the monitors say “Ready,” and do the test. Ensure all monitors display “Ready” and fix any warning lights or Diagnostic Trouble Codes (DTCs).